Improved diagnostic methods are needed for human filariasis to detect early infections and to monitor the efficacy of vector control, drug therapy, and future vaccines. Our successful development of a sensitive and specific parasite antigen assay for canine dirofilariasis led to studies to develop and evaluate similar tests for human filariasis. Progress to date has included the identification of a 200 kD parasite antigen in sera from patients infected with Wuchereria bancrofti and development of a monoclonal antibody-based ELISA for this antigen. Field studies conducted in South India demonstrated that this assay is more sensitive than microfilaria detection, that it provides a species- specific diagnosis, and that it is practical for use in developing countries. The first specific aim of this proposal is to more fully explore the practical value of the W. bancrofti antigen assay as a clinical and epidemiological tool for bancroftian filariasis. We will continue to study the significance of parasite antigenemia in "endemic normals" and assess antigen detection as a test of cure after drug treatment. We will also expand our field studies to evaluate the test in different endemic areas. The second specific aim of this proposal is to develop and evaluate antigen diagnostic tests for brugian filariasis and onchocerciasis. Our expansion into the area of onchocerciasis is justified by a general recognition that improved diagnostic methods are needed to monitor transmission in the era of vector control and ivermectin. Parasite antigens containing the phosphorylcholine epitope have been demonstrated in sera from humans and animals infected with O. volvulus and B. malayi. Unfortunately, assays based on detection of these antigens with monoclonal antibodies to phosphorycholine have been insensitive because of antibody competition. Additional work with new approaches is needed. Our third specific aim is to test the hypothesis, based on observations in humans and experimental animals, that antibodies to circulating parasite antigens may have a role in protective immunity in filariasis.